DFT Approaches Unraveling Atomic Structures and Incorporation Selectivity of Dicarboxylic Acids in Octacalcium Phosphate

ABSTRACT Octacalcium phosphate (OCP) containing organic molecules like dicarboxylic acids is promising because its properties are expected to be designed by the incorporated molecules. From the first discovery of succinate‐ion–incorporated OCP, a number of OCP systems incorporating dicarboxylate ions were reported, and incorporation selectivity depending on the methylene‐group numbers of the dicarboxylate ions was found. However, not only the origin of the selectivity but also even their detailed atomic structures were poorly clarified. For this purpose, DFT calculations were performed for a series of dicarboxylate‐ion–incorporated OCP systems. A data‐driven type optimization method was employed and combined with DFT to explore low‐energy atomic structures of OCP with different dicarboxylate ions. It is found that calculated d 100 values of the most stable atomic structures are in excellent agreement with experiment, demonstrating the linear correlation with methylene‐group numbers of the dicarboxylate ions. Calculated formation energies of the systems show an odd‐even effect on their incorporation stability against the methylene‐group numbers, which is also in reasonable agreement with experiment. Such a trend in formation energy can be explained in terms of local atomic coordinations between Ca ions and carboxy groups of the dicarboxylate ions. These results prove the effectiveness of our computational strategy for such complicated organic and inorganic composite systems.